Treating waste and low-grade pigments



Patented Sept. 23, 1930 PATENT orrlca HUGO REINHARD,'OE OIBERHA'USEN, GERMANY TREATING WASTE AN D LOW-GRADE PIGMENTS No Drawing. Application filed September 8, 1928 Serial l io. 304,836, and in Germany September 9, 1927.

This invention has reference to a method of manufacturing and treating mineral pigments by means of which the percentage of waste or inferior by-products may be reduced and the by-products in the course of manufacture may be converted into a state of high commercial utility. It is'well known that in the manufacture of mineral pigments, particularly oxides or oxidic combinations of 10 metals, the occurrence of a comparatively large percentage of inferior .by-products,

" which are deficient in granulation purity, flufliness or specific gravlty, is unavoidable. In accordance with the previous art it has,

for instance, been suggested in the case of oxidic pigments, such as oxide of zinc, to separate the inferior by-products in the wet way by treatment with water, salt solutions or the like, or by pneumatic means, but the results accomplished were highly unsatisfactory, inasmuch as the treated by-products never attainedthe degree of fine distribution, color, fluifiness and the other valuable properties of, the unstained superior kinds of pigments obtained directly either by the burning of the metal with hot air or oxygen, or by a similar treatment of the re spective metallic ores or by the indirect-process of reduction, distillation or vaporization of the zinc and of equivalent metals yvith consequent combustion. Usually the low grade heavier and darker admixtures were not car: ried away bythe'blast by which the. bright, unstained, impalpable portions of the oxidation products were driven oif fromthe residue of raw material, andthese heavier and darker admixtures wouldaccumulate, with appreciable percentages of fine oxide, in the corners and recesses of the combustion and treating chambers as so-called dropoxide or waste-oxide, and being comparatively too heavy to be carried away by. the

blast, they were deposited in the first sec-' tions of thechamber system, and their quality was in most cases further impaired by admixtures of the waste dust existing in the various enclosures of the plant.

, In. view of these difiiculties encountered in the separation of the inferior grades of oxidic from the more finely dispersed particles by 1 and covering qualities.

and similar pigments, which were increased in the case of the wet treatment by thenecessity of drying the products, it has been usual to dispose of these inferior grades by mixing small quantities thereof with the re 4111 production of the better grades of pigments.

Now my invention refers to a novel-treatment of these waste products, drop oxides and the like, which broadly comprises treating them with the usual vehicles of paints and the like, such as oils, among which I maymention the various kinds of linseedoil and equivalent oils, stand-oil, refined, v thickened and bleached poppy oil, fish oil, and other oils and varnishes usually employed as vehicles in the preparation of paints andthe like. By means of this treatment the waste products become directly available, and in view of the very uniform dispersion of the waste products mentioned in such vehicles, as contradistinguished from their dispersion in aqueous liquids, the coarser particles may be readily separated stirring and more or less prolonged settling. 5

Preferably. this agitation with consequent separation of the coarser particles may be eifected by the process of centrifuging, making use of the usual centrifugal separators. ,By this means it becomes possible to separate from the mixture of the pigments with oil in which the pigments are contained insuspension, the coarser and usually darker colored or discolored particles which may be employed in the manufacture of cheaper grades of paints and coatings, such as rust preventing paints and the. like, while the finely dispersed. portions,- containing: the

finely disintegrated or powdered pigment suspended therewith in the larger proportion of the oil, areobtained separately and providea stock base or: composition which may be used directly for the manufacture of a high grade. paint or varnish of good color According to a preferredmanner of carrying out my new method of treatment I may proceed by first subjecting the inferior or waste. products of the manufactureof pig- 7 ency, this may be adjusted by the addition of ments to screening and mechanical disintegration in any succession of steps, by whichmeans the finest particles. of the pigments, oxide of zinc, for instance, are first separated from the'coarser particles and from deleterious admixtures before the treatment with oils andthe like, so as to eliminate the lower grades of material and the foreign substances as much as possible. Thereupon the one or 0 other class of material obtained by this separation may be submitted to the treatment with oils according to this invention, and they are thoroughly stirred up and mixed therewith, so as to cause the solids to be suspendedin the oilin a highly dispersed state. The impurities and unoxidized metallic particles present as well as the darker portions of the oxidic products and foreign substances being generally coarser or heavier than the fine and more readily ,suspended portions of the oxide of zinc, it is ossible by this means, and particularly by t e aid of centrifuging, to eliminate the inferior particles and the impurities and foreign bodies from the mixture almost completel and without any appreciable loss of the ner portions of pigment. The separation may be carried .on, so as to obtain different degrees of fineness of product, by alterin the velocity of the centrifugal separator, ut ordinarily it will be found sufficient to run the separator at a moderate speed. Usually the amount of oil necessary for the separation by differentiation of dispersion, or for the carrying on of the centrifuging method will be found to correspond to the amount required for the fin-.

ished paint made from the finer portions of the material under treatment. In case the mixture should not possess the proper consistmore pigment or more of the oil vehicle. By thus adjusting the consistency of the mixture .the efficiency of separation in the different stages of agitation or centrifuging may also be increased. In order to arrive ata still greater differentiation and fineness of prodnot, the residues of the several stagesrof agitation or'centrifuging, particularly-of the first stage, may be submitted over again to the agitating and centrifuging procedure after an addition thereto of the oil and, if

necessary, after grinding of the residue one the stages is of suficient' fineess, it may be used or more times'in the oil contained therewith. In case the residue remaining, in some of directly for the manufacture of paints -or.var-' -nishes by grinding it up or otherwise mixing .it with a suitable vehicle; or it may be previously ground alone or'in admixture with oil until therequired degree of fineness has beenobtamed.v

H u of the raw material (drop oxide) showszp '1 Zn-77 .60 (calculated as ZnO: 96:61) Pb 0.135 Cd 0.113 SiO 0.52 (3:10 0.084 F 0 0.37 0.073 A1 0 0.12

However, the 77.60% Zn contains up to 5% of metallic zinc, so that approximately only about 72% of the raw material in the form of Zn can be used for the manufacture of paint. Such 72% of Zn would be equivalent to about 91.16% ZnO. The first centrifumaterial contained in theofi-products or byproducts or drop-oxidesthan it is possible to produce b the old, ordinary process of screening an bolting, and there is the further advantage that the new process-accordingto this invention may be conveniently combined with the usual methods of separation by screening, bolting and by pneumatic and similar means, and it becomes possible thereby to economically recover the by-prodnets and to utilize the waste resulting in the manufacture of pigments and the like, and to convert such waste and off-product into material of high commercial value and utility, and there is practically no waste that cannot be utilized inasmuch as even the worst kinds of admixtures may be separated out and utilized as rust-preventing paint or for similar purposes. e

The invention has been described herein in its broad features only, and it should be understood that it may; be modified and be embodied in other exemplifications within the scope and-spiritof the appended claim.

'Iclaim:- a v The process of recovering waste or low grade products resulting from the manufacture of zinc oxide and utilizing the same for the manufacture of oil, enamel or'lacquer acter and amount to produce the desired paint, and centrifuging-the mixture so as, to efi'ect an elimination o the coarser solid articles. and-toleave the finer solid particles combined with the vehicle to produce a paint 

